Paper is made by a continuous process on a papermaking machine. Paper is formed at the wet end typically by depositing a slurry of paper fibers and water on a screen. The mat of fibers on the screen is dewatered by press rolls and suction boxes and transferred to a progression of rollers where it is pressed and dried. The final forming step is to run the web of formed paper through a calender or super calender which compresses the web between opposed rollers and improves the surface finish and the uniformity of paper thickness. All the processes involved in papermaking, from the forming of the paper at the wet end to calendering at the dry end are continuous in nature and each length of the paper is subjected to the same processes and forces, thus forming a paper web of high uniformity. However, the final step in the papermaking process, that of winding or reeling the paper web onto spools for removal from the papermaking machine, can result in non-uniform treatment of the paper web.
The reel of paper typically formed on a modern papermaking machine may have a diameter of 120 inches or more and a reel width of 200 to 400 inches. The paper on the so-called machine or jumbo reels is typically further processed by rewinding and slicing and sometimes coating the paper to form individual reels or sets to be used by paper-consuming customers such as newspapers. Studies performed in the past few years have shown that a paper web formed into the jumbo or machine reel can become damaged. The damage typically is in the form of tears near the edge of the sheet or creasing near the center. The damage typically results in the paper web breaking when it is further processed in a paper coating or rewinding machine or is utilized in a printing press.
A set is a smaller reel or roll of paper which has been formed from a jumbo reel. The last set is paper which is nearest the center of the reel, that is that paper first wound onto the reel spool. Studies have shown that at some paper mills, as high as 70 to 80 percent of all rejects on critical paper grades are from the last set off the reel. In one study, 73 percent of the press room paper web breaks during printing were in the last set off the reel, that is in the paper that was closest to the spool when the paper was wound in to a jumbo reel.
With increased papermaking speed and web widths, the size and weight of wound jumbos has also increased. In the past a certain percentage loss of paper due to reel defects was considered acceptable. However, with an increase in size of machine rolls, the problems associated with existing paper reels has been exacerbated while at the same time tolerance of product defects or waste of any kind has decreased due to increased competitive pressures and concern for maximum efficiency in the utilization of natural resources.
The solution to defects in the machine or jumbo reel is to produce a more uniformly wrapped paper web on the reel. The tightness or quality of the reel wrap depends on three factors: Tension, Nip pressure (including reel support for uniformity of nip pressure), and Torque. A paper winder employs a reel drum which is driven by the paper machine drive at a speed selected to impart a proper amount of tension. The tension is selected for a given grade and strength of paper and is typically 10-25% of the tensile strength of the given grade of paper. The web spool and the reel of paper built up thereon rides against the reel drum forming a nip therebetween. The nip compresses the paper which is wound onto the core. At the same time, the reel drum provides support at initial winding of the reel, the support continuing but diminishing as the jumbo reel increases in size.
Tension may be controlled by a centerwind assist drive which drives the machine reel. The centerwind assist is a differential torque drive with the differential torque controller controlling the amount of tension introduced into the web between the reel drum and the machine reel as it is built up on the core. European Patent Application Number 91850261.8 entitled "Reel-up and Method for Regulation of the Nip Pressure in a Reel-up" (Publication No. 0 483 093 A 1, published on Apr. 29, 1992) discloses a reel system which addresses some of the foregoing problems in the reel. The European Application disclosed employing a tilting rail which is pivoted about the axis of rotation of the reel drum. Riding on the reel is the core of the reel upon which the paper web is wound. The European Application discloses varying the angle between the rails and the horizontal such that the load of the nip formed between the machine reel and the reel drum remains uniform as the web is wound onto the machine reel.
Another type of winder system is the TNT.TM. System produced by Beloit Corporation and employs continuous control of the tension, nip and torque to produce machine reels of uniform density which are substantially less susceptible to the problems discussed herein. The Beloit TNT machine employs a horizontal rail located above a reel drum. The reel drum is vertically positionable and is controlled in response to a load cell which directly measures the nip pressure. The Beloit TNT machine solves the problems outlined above and produces a machine roll of uniform structure with minimal winder induced defects. Although the Beloit TNT machine provides a satisfactory solution to producing jumbo machine rolls of excellent uniformity, other approaches to the same problem are desirable. The papermaking industry has a large base of installed machinery of many differing makes and ages which are utilized to make a wide variety of papers and paper boards. Thus, more than one solution to a given problem may be advantageously employed.
What is needed is another approach to designing a winder with improved machine winder uniformity.